Strategies to keep cats from melting

[J17GT]

I emailed Whipple today to ask if there was anyway to tell when cat protection kicks in. They said the only way to know would be with a wideband and you can watch the air fuel ratio.

He then finished the email with this when I asked about drag racing:

"I will say, you will be in cat protection when you're at WOT after roughly 4 seconds, the temp climbs extremely fast at this power level so drag racing, you'll by from mid track on in cat protection."

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[engineermike]

With HPscanner you can log the fuel source and see when it goes into “exhaust temperature control”.

The neat thing about the stock calibrations is the spark timing will automatically advance when lambda goes rich for cat protect, so you get some of the lost power back. Whipple disables this in their cal though.

 

[IamCDNJosh]

Is there a relationship between CR and EGT's running boost?

Curious since the predator is 9.5:1 and the coyote 2 & 3 being 11:1 and 12:1 respectively.

 

[engineermike]

Is there a relationship between CR and EGT's running boost?

Curious since the predator is 9.5:1 and the coyote 2 & 3 being 11:1 and 12:1 respectively.

All things being equal a lower compression ratio will have a higher egt. However, all things are rarely equal. The Predator, due to the low compression, can run significantly more spark advance so the egt comes back down. Coyotes running 14-16 deg spark doesn’t help our cats live at all.

Perhaps that is a key to all this. Figure out how to run more spark timing (xdi pump and/or interchiller) and the cats should live longer.

 

[Torinate]

All things being equal a lower compression ratio will have a higher egt. However, all things are rarely equal. The Predator, due to the low compression, can run significantly more spark advance so the egt comes back down. Coyotes running 14-16 deg spark doesn’t help our cats live at all.

Perhaps that is a key to all this. Figure out how to run more spark timing (xdi pump and/or interchiller) and the cats should live longer.

So would using meth injection help in dropping temps?

What’s too hot?

Is the PID CatTemp accurate at all?

The statement earlier about whipple cat temps going up quickly is completely accurate! I’ve seen them jump 800* in 2 seconds under boost. They come down quickly after, but not like they rise.

What’s the difference in the cells? Is more better?

In looking at the Gesi website, the higher the cell count the higher hp they could handle. However, a different thread here someone said to use a 200 cell.

 

[engineermike]

@Torinate I don’t believe meth by itself reduces egt but if you run more spark timing then the egt will fall some.

The coyote and Predator both turn on exhaust temp control at 1650 F.

The cat temp PID is probably very accurate for the stock combination but that’s about it.

 

[Torinate]

Appreciate that. Likely not so accurate then running the blower. I can’t remember the Max I’ve seen with the PID but it’s been much higher than 1650. I’ll have to wait until spring when I get the car back out for a good read.

 

[shogun32]

mixing outside air into the exhaust would seem like a solution (AIS), it would also flash-burn left over fuel to boot. But if there's too much of that then air temps go even higher.

 

[engineermike]

I’ve thought about cooling fins or heat sinks ahead of the converters as well. The gen3 seems to eat #2 cats at a higher rate than #1. Could it be because the #1 has a flange ahead of it that acts as both a sink and a fin, helping to cool the exhaust gas? Not sure...but possible.

 

[sk47]

mixing outside air into the exhaust would seem like a solution (AIS), it would also flash-burn left over fuel to boot. But if there's too much of that then air temps go even higher.

Hello; I do not see how this could work to help a cat. The pressure inside the pipes between the engine and the cats would be high compared to outside air. Any opening would wind up being an exhaust leak unless the air was pressurized.

I do get why from a pure performance point of view some were getting the cat delete pipes. It has to figure any restriction in the exhaust will hurt performance. Of course the down side of a cat delete will be increased air pollution. I suppose the problem was folks using these setups on street driven vehicles.

There was a time when I saw a similar thing on diesel pickups. I think they called it "burning coal". The trucks would blow thick black clouds of exhaust. Never mad e much sense to me and smelled bad.

 

[shogun32]

The pressure inside the pipes between the engine and the cats would be high compared to outside air. Any opening would wind up being an exhaust leak unless the air was pressurized.

well yes it would have to be pressurized or at least have a check-valve so it would draw air on the negative pulse wave.

 

[sk47]

well yes it would have to be pressurized or at least have a check-valve so it would draw air on the negative pulse wave.

Hello; Not sure there is a negative pulse wave in the exhaust at all. There are of course pulses as the cylinders are evacuated but do doubt there are any times the inside of the exhaust pipes have a negative pressure. I have always figured constant above ambient air pressure inside the pipes. Interesting idea if it is workable.

Might be that a double walled exhaust pipe could be made with air pumped in to the outside portion where there is no exhaust pressure at all. I owned a 1972 Porsche 914 back in the 70's. Fun to drive but had lots of issues. The heat systems were double walled header pipes. The inner pipe was a heavy normal pipe. The outer wall was thin sheet metal bent to wrap around the inner pipe. It had openings so a fan could blow air thru for heat. After a few years the thin sheet metal would start to rust and have too may holes so I only had good heat going up a hill. Eventually aftermarket systems were made from stainless steel, which was dandy and long lasting. Any way a lot of heat could be pulled from a header pipe that way.

 

[markmurfie]

It comes down to sizing the catalytic converters appropriately for the power the engine is going to make. They still need to work when the engine is first started up and is cold, and in low power demand operating conditions. So they can't be oversized.

Basically buying and installing bigger catalytic converters Is a huge PITA, to damn near impossible to do it legally with the current CARB and Federal laws.

So we are stuck with making as much power with the stock exhaust manifolds. (cause one side has it built into it). Twin turbo kit companies are not something I would invest in right now, cause thats going away just like the "off road" stuff. No one wants a CAT in front of their turbo.Koenigsegg has a patented solution for this.

My answer:
EGT sensors before and after the CATs, collect data with logs, send it to your tuner and have them tune the COT protection. Hopefully they know a safe, risky, dangerous, and certain death temperature range and don't use your car, money, and a few sets of CATs to figure that out. Yeah you would pick up 200-300HP by going to catless, but this is the world we live in now if you want to be street legal and still make 1000+HP.
Maybe in the future we will have some external CAT temperature control system that lets us rely less on COT and choking the combustion chamber in fuel. Like an exhaust fluid injection kit like the diesels do. That doesnt effect what the O2 sensors read or their life expectancy.

 

[engineermike]

I happened onto something interesting. We know that cat overtemp protection kicks in and richens the A/F ratio up to the low .7's to protect the cats. This is a stock feature and the aftermarket supercharger companies keep it active. I checked a few other vehicles to see how the factory does it when forced induction is used and noticed something interesting, all at WOT:

Stock Gen3 coyote: Commands .85 lambda at low rpm and .82 at high rpm. COT cannot command richer than .72 (combustion stability limit). Many aftermarket supercharge cals attempt to keep these same or similar targets, as they are good for power.

Ford Predator: Commands .85 lambda at low rpm and .75 at high rpm. COT cannot command richer than .68. It runs close to the Coyote's COT lambda even before going into COT.

Ford GT supercar: Commands .87 lambda at low rpm and .72 at high rpm. COT cannot command richer than .70. It already runs nearly COT lambda before COT cuts in.

Ford Raptor: Commands .87 lambda at low rpm and .70 at high rpm. COT cannot command richer than .68.

Hellcat: I'm not as familiar with Hellcat tuning, but my interpretation is that it commands .85 lambda at low rpm and .70 at high rpm. COT cannot command richer than .66.

The point of all this is that the factory forced induction cars command nearly COT lambda at WOT so they are less likely to enter COT mode.

 

[Torinate]

Interesting indeed. So there’s already a built in “margin of error” in their tuning. We know lean is mean, however, rich is safe.

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